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Bio-mediated Geo-material Strengthening for engineering applications

Periodic Reporting for period 2 - BIOGEOS (Bio-mediated Geo-material Strengthening for engineering applications)

Reporting period: 2020-05-01 to 2021-10-31

BIOGEOS deals with the study, development, and characterization of biocementation processes destined for civil engineering applications. Earth materials, or commonly referred to as geomaterials, hold a crucial role in all building works as they provide the foundation for all kinds of infrastructure. To safeguard infrastructures, engineers need to ensure that their foundations can resist natural hazards among which earthquakes or erosion, caused by extreme and recurrent weather events. Traditional practices rely on the use of artificial cement or petroleum derivatives which are mixed with the underground environment to strengthen foundations. However, there have been increasing concerns around the environmental impact of such admixtures and their carbon footprint owed to energy-intensive operations. BIOGEOS develops new knowledge and breakthrough research to characterize and develop an alternative strengthening process for geo-materials based on nature-inspired biocementation.

To describe the way biocementation is created, its evolution over time and its ultimate material properties, one needs to first capture the contributing mechanisms behind it. These entail metabolic activities of microorganisms, flow, and transport phenomena as well as chemical reactions. Further, one needs insights into the biocemented material’s internal architecture, on the order of micrometers, as the location and morphology of biocement can drastically affect the resistance of the strengthened materials.

Similar microorganisms are used in several applications, in food and pharmaceutical sectors in particular. Our principal objective is to characterize the activity of these microorganisms harnessing the latest advances in experimental tools which have not been used in the fields of civil engineering before. More precisely, in our laboratories we have developed tools and processes which study transport and reaction phenomena using high resolution microscopy techniques on microchip porous devices or computed microtomography observation techniques. Further, we inspire from advances in other fields of science to apply and characterize biocementation using notions and techniques of micro-encapsulation or electrocatalysis, for example. BIOGEOS is a widely multidisciplinary project and requires the simultaneous study of complex multiphysical mechanisms across scales. The three work packages of the project cover: (i) micro-scale investigations; (ii) geotechnical lab-scale studies and (iii) numerical works. These latter range from the development of algorithms for robust characterization of flow, reaction phenomena, to image processing techniques and to the simulation bio-geo-hydro-chemical systems to predict the application of biocementation in typical geotechnical and geoenvironmental works.
How can we create built environments that serve our societal purposes while helping combat the existential threats to our planet? We think that the answer lies in living material technologies that harness the building potential of biological systems in ways that are inspired by nature. Microbial induced calcium carbonate precipitation (MICP) is a promising technology that yields bacterially produced calcium carbonate within a matrix and leads to enhanced mechanical properties. However, the degree of control over the amount, location, and structure of the forming calcium carbonate remains insufficient for civil engineering applications. Here, we demonstrate that the amount and location of calcium carbonate produced within a matrix, can be controlled through the concentration and location of bacteria; these parameters can be precisely tuned if bacteria are encapsulated within biocompatible hydrogels.

To control the timing of the release of calcium ions that are weakly bound to the hydrogel matrix without compromising bacterial viability, we exploit a new competitive ligand exchange that relies on the presence of. This concept highlights, for the first time, the potential to program the release of the biochemical yeast extract machinery of MICP, with the recognition of a component that is inherently specific to the solution used to promote bacterial growth. We take advantage of the formation of biologic calcium carbonate at well-defined locations to form load-bearing biomineralised hydrogel-sand scaffolds with a uniaxial compression strength that is two times higher than that of hydrogel-sand scaffolds and 35 fold higher than that of sand alone.

Overall, The project has been managed on different fronts, which represent the various work packages and research tools:
a) At the micro-scale study, one necessary step was to observe, in real-time the initiation and time-evolution of bio-cementation from the moment microorgnisms flow into porous media until they grow, multiply and eventually precipitate biocement. This characterization was achieved through video microscopy on microfluidic devices and subsequent development of image processing algorithms which have been used to characterise the observed temporal and spatial phenomena involved in bio-cementation. First results have been analyzed and published.
b) We have further unravelled the influence of applied direct currents on the process of biocementation. Among the published results we presented extensive crystalline characterization analysis and observed the effect of electric currents and various chemical conditions on the precipitated morphology.
c) We have developed a novel system to produce biocementation agents in the form of microcapsules which are activated under controlled environments to release cargo capable of creating biocementation.
d) Several new results have been obtained, among which, on the quality assesement and quality control of biocementation at the scale of real geotechnical works. For the first time we have coupled electrocatalysis of CO2 to generate a substrate for biocementation. The findings are promising towards developing a system which uses CO2 as intake and produces biocement as end product. We have also demonstrated how biocementation adapts to a variety of base materials and porous networks in column experiments.
BIOGEOS introduces novel research approaches, tools and the combination of multiphysical systems which are beyond the state of the art in civil engineering and geotechnical research.
More precisely,
a) our team is in unique position to advance the knowledge around reactive transport phenomena of biocementation and their spatio-temporal evolution thanks to the experimental set-up which combines video microscopy and microfluidic devices in meter-long flow trajectories.
b) the BIOGEOS large-scale experiment, which has already accommodated 200 m3 of geomaterials and is delivering new knowledge on the application and monitoring of biocementation at the representative scale of engineering works.
c) the coupling of electric currents, electrocatalysis and notions of microencapsulation and controlled biocementation activation to push the boundaries of traditional biocementation practice.
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